Pyroelectric sensor basics

     Pyroelectric infrared sensor is capable of detecting human or animal infrared light emitted by the output electrical signal. As early as 1938, it was proposed the use of pyroelectric effect detecting infrared radiation, but not taken seriously until the '60s, with the laser, infrared technology is developing rapidly, it can also promote the pyroelectric effect on research and pyroelectric crystals for applications. Pyroelectric crystal has been widely used infrared spectroscopy, infrared remote sensing and thermal radiation detectors, it can serve as an ideal infrared laser detectors. It targets is being widely applied to various automation control devices. In addition to our well-known corridor automatic switch, burglar alarm been applied, the field of application of the more promising. For example: In the room no one will stop automatically when the air conditioner, water dispenser. TV viewers can judge no one has to sleep after watching or automatic shutdown mechanism. Turn on your monitor or automatic doorbell on the application. Combined with video cameras or digital camera automatically records the animal or human activities, etc. ....... You can own whimsy, combined with other circuits develop more outstanding new products. Or automated control devices.

Pyroelectric sensor basics

    Pyroelectric effect similar to the same piezoelectric effect, is due to temperature changes caused by the crystal surface charge phenomenon. Pyroelectric sensor is a temperature-sensitive sensor. It is a ceramic oxide or a piezoelectric crystal element composed of two surfaces formed on the element electrodes of the sensor within the scope of monitoring the change in temperature ΔT, pyroelectric effect will be on the two electrodes generates an electric charge ΔQ, i.e. between the two electrodes to generate a weak voltage ΔV. Due to its high output impedance, in the sensor there is a FET for impedance transformation. Pyroelectric effect charge generated ΔQ is the combination of ions in the air disappear, i.e. when the ambient temperature is stable constant, ΔT = 0, the sensor no output. When the body enters the detection zone, because the body temperature and ambient temperature difference, resulting ΔT, there ΔT output; when the body does not move into the detection zone, the temperature does not change, there is no output of the sensor. Therefore, this sensor detects human or animal activity sensing. From the experimental evidence, the sensor without optical lens (also known as the Fresnel lens), the detection distance is less than 2m, and coupled with an optical lens, its detection distance can be greater than 7m.

Use should pay attention to the following points:

     A. DC operating voltage must meet the requirements of our values, too high and too low will affect the module performance, and requires well-regulated power supply must be filtered, such as computer USB power, mobile phone charger power, older 9V laminated battery Modules are unable to meet the job requirements, customers are advised to use the power transformer and after three terminal regulator chip voltage regulator and then through 220UF 0.1UF capacitor filtered power supply.

     B. as far away from the body when debugging sensing area, although sometimes the body is not in front of the module, but too close to the body when the module from the module can also be sensitive to the cause has been output, as well as commissioning Do not touch the circuit part of the body can also affect module , more scientific approach is the output is terminated with a LED or a multimeter, the module is covered with a newspaper, people leave the room, and so after 2 minutes to see whether the module or has been output?

     C. the module does not work properly when connected to the load, the load connected to work after disturbance, One reason is because the power supply capacity is relatively small load, the load voltage fluctuations caused by work cause the module to malfunction, and the other reason is that the load was electrical work can cause interference, such as relays or solenoids and other inductive load will produce reverse electromotive force, 315M transmitting plate work will be electromagnetic radiation will affect the modules. Solution is as follows: A, power supply plus filter inductor. B, using load and modules using different voltages, for example: Load a 24V operating voltage, the module uses 12V operating voltage, during a three-terminal regulator isolation. C: Using larger capacity power supply.

     D. the human body sensing module can only work in the room and the work environment should avoid sunlight, direct exposure to intense light, and if the working environment has a strong RF interference, shielding measures can be used. In case there is a strong air turbulence, close windows and doors or prevent convection. Sensing area to avoid facing the heating appliances and objects as well as easily windblown debris and clothing.

     E. the human body sensing module is recommended to install in a sealed box, or it may have been the output signal.

     F. if the request body sensor module detection angle less than 90 degrees, the lens can be obscured by opaque tape or crop reduction lens to achieve.

     G. body sensor module using dual probe, the body's limbs and head movement direction and sensor sensitivity is closely linked to, and determine the characteristics of the infrared modules can not be precisely controlled sensing distance.

     H. probe module (PIR) can be flip-chip on the other side of the circuit board. The probe can also be used to extend core shielded cable, length should be 20 cm or less as well.